In U.S. Pat. No. 4,391,773 there is decribed a negative field generator having utility in the purification of air. The generator which is described in that patent includes a field emitting device in the form of a flat solid dielectric material on the opposite faces of which a pair of electrodes are respectively disposed. When a high frequency, high voltage source is connected across the electrodes, a high intensity, high frequency negative field is developed in the space surrounding the field emitting device, and this negative field causes airborne solids to precipitate out of the surrounding air.